TWI762073B - Quartz glass crucible and method of making the same - Google Patents

Abstract

The present invention provides a quartz glass crucible capable of suppressing the peeling of the brown ring and improving the yield of silicon single crystal and a manufacturing method thereof. The peak of the distribution in the depth direction from the inner surface 10i of the total concentration of Na, K, and Ca of the quartz glass crucible 1 of the present invention exists at a position deeper than the inner surface 10i.

Description

Quartz glass crucible and method of making the same

The present invention relates to a quartz glass crucible and its manufacturing method, in particular to a quartz glass crucible used for pulling silicon single crystal by the Czochralski method (CZ method) and its manufacturing method.

Quartz glass crucibles are used in the production of silicon single crystals by the CZ method. In the CZ method, a silicon raw material is heated in a quartz glass crucible to melt it, a seed crystal is immersed in the silicon melt, and the seed crystal is gradually pulled while rotating the crucible to grow a single crystal. In order to manufacture high-quality silicon single crystals for semiconductor devices at low cost, it is necessary to improve the single crystal yield in a single pulling process, so a crucible that can withstand long-term use and is stable in shape is required.

In recent years, as the diameter of the silicon single crystal has increased, the pulling operation time of the single crystal has become very long. If the inner surface of the quartz glass crucible is in contact with the silicon melt above 1400 ℃ for a long time, it will react with the silicon melt to crystallize, and a brown ring-shaped cristobalite called brown ring will appear. There is no cristobalite layer in the brown ring, or even if there is a very thin layer, but with the passage of operation time, the area of the brown ring continues to expand, merge with each other, and continue to grow, and finally its center is eroded and becomes irregular. The glass melted out. If the glass melting surface appears, the silicon single crystal is likely to be dislocated, thereby deteriorating the single crystal yield. Therefore, a quartz glass crucible in which brown rings are not easily generated and is not easily grown even when brown rings are generated is desired.

As for the method of suppressing the generation and growth of the brown ring, for example, Patent Document 1 describes a method in which a layer having a high reactivity with a silicon melt is formed in the inner layer of a quartz crucible, and the melting loss rate is The formation of nuclei is fast, thereby reducing the brown ring. In addition, Patent Document 2 describes a method of increasing the number of brown rings generated at the oscillating position of the melt surface by etching or sandblasting the oscillating position on the surface of the melt, thereby increasing the oscillating position on the surface of the molten metal. The number of brown rings produced below is reduced.

In addition, Patent Document 3 describes a quartz glass crucible in which the OH group concentration of the surface glass layer with a thickness of 100 μm from the inner surface of the crucible is set to 90 ppm or less, and the thickness of the lower part is 1 mm from the inner surface of the crucible. The OH group concentration of the glass layer is set to 90-200 ppm. That is, by reducing the OH group concentration of the shallower surface layer of the inner layer of the crucible, the melting rate of the quartz glass is slowed down, so that the nuclei of the brown ring are likely to remain, and by further reducing the shallower surface layer The OH group concentration of the layer on the lower side becomes higher, and the crystal nucleus is easily grown, thereby suppressing the peeling of the brown ring.

In addition, Patent Document 4 describes a technique in which a vitreous silica crucible having a straight body portion and a bottom portion is provided with an innermost layer including a _SiOx film having a thickness of 0.5 to 200 μm (0<x<2 ); an inner layer, comprising transparent silica glass, and having an OH group concentration of less than 30 ppm and a thickness of 3 to 5 mm in an area in contact with the innermost layer; and an outer layer, comprising opaque silica glass; And the inner surface of the crucible is pre-coated with the innermost layer which becomes the sacrificial layer. Even if the crystal nuclei of cristobalite are formed on the surface of the innermost layer before the polysilicon is completely melted, if the innermost layer is dissolved in the silicon melt faster than the rate of crystallization in its vicinity, it can be suppressed in the innermost layer. Crystal nuclei of cristobalite are formed on the surface of the inner layer exposed after melting, thereby suppressing the generation and growth of brown rings, which are the cause of lowering the yield of silicon single crystal pulling. Prior Art Documents Patent Documents

[Patent Document 1] Japanese Patent Laid-Open No. 2005-306708 [Patent Document 2] Japanese Patent Laid-Open No. 2005-320241 [Patent Document 3] Japanese Patent Laid-Open No. 2009-161364 [Patent Document 4] Japanese Patent Laid-Open No. 2012-136400

[Problems to be Solved by Invention]

As described above, during the pulling process of the silicon single crystal, the brown ring is formed on the inner surface of the quartz glass crucible. When the brown ring is peeled off from the inner surface of the crucible and mixed into the silicon melt, there is a possibility that the yield of the silicon single crystal will decrease, so it is necessary to suppress the peeling of the brown ring.

Therefore, the object of the present invention is to provide a quartz glass crucible capable of suppressing the peeling of the brown ring and improving the yield of the silicon single crystal, and a manufacturing method thereof. [Technical means to solve problems]

The inventors of the present application have repeatedly researched the mechanism of the generation, growth and peeling of the brown ring, and found that in order to suppress the peeling of the brown ring, it is important to reduce the number of brown rings as much as possible. To make it grow stably, by adjusting the distribution of Na, K, and Ca in the depth direction near the inner surface of the crucible, the reduction in the number of brown rings and stable growth can be achieved.

The present invention is based on such technical findings, and the silica glass crucible for pulling a silicon single crystal of the present invention is characterized in that a peak of the distribution of the total concentration of Na, K, and Ca in the depth direction from the inner surface exists. at a position deeper than the above-mentioned inner surface. According to the present invention, the generation of brown ring nuclei occurring on the inner surface of the crucible can be suppressed. Therefore, the growth and peeling of the brown ring can be suppressed, and the yield of the silicon single crystal can be improved.

The peak of the total concentration of Na, K, and Ca in the quartz glass crucible of the present invention preferably exists within a depth range of 32 μm or less from the inner surface, more preferably 16 μm or more and 32 μm or less from the inner surface. within the depth range. Thereby, the melting speed of the inner surface of the crucible can be faster than the growth speed of the brown ring nucleus, so that the brown ring nucleus disappears. Therefore, the growth and peeling of the brown ring can be suppressed, and the yield of the silicon single crystal can be improved.

In the present invention, the peak value of the total concentration of Na, K, and Ca within a depth range of 16 μm to 32 μm from the inner surface is preferably Na, K, and Ca within a depth range of 0 μm to 8 μm from the inner surface. 2 times or more and 19 times or less the average value of the total concentration of K and Ca. Thereby, the generation and growth of the brown ring nucleus can be suppressed.

In the present invention, the average value of the total concentration of Na, K, and Ca within a depth range of 32 μm to 1000 μm from the inner surface is preferably Na within a depth range of 0 μm to 8 μm from the inner surface. , 0.6 times or more of the average value of the total concentration of K and Ca and not more than 1 time. In addition, the total concentration of Na, K, and Ca in the depth range of 32 μm or more and 1000 μm or less from the inner surface preferably has a negative concentration gradient when the depth direction is a positive direction, and more preferably has a negative concentration gradient of -8.2× Concentration gradient below 10 ¹⁰ atoms/cc/μm. Thereby, the melting of the inner surface of the crucible can be suppressed, the brown ring can be stably grown, and the peeling from the inner surface can be suppressed.

In addition, the silica glass crucible for pulling silicon single crystal according to another aspect of the present invention is characterized by having: a first surface layer part provided in a depth range of 0 μm to 16 μm from the inner surface; and a second surface layer part, It is provided within a depth range of 16 μm to 32 μm from the above-mentioned inner surface; and the third surface layer portion is provided within a depth range of 32 μm to 1000 μm from the above-mentioned inner surface; The maximum value of the total concentration of Na, K, and Ca is higher than the maximum value of the total concentration of Na, K, and Ca in the first surface layer portion.

According to the present invention, the generation of brown ring nuclei occurring on the inner surface of the crucible can be suppressed. In addition, the melting rate of the inner surface of the crucible can be made faster than the growth rate of the brown ring nucleus, so that the brown ring nucleus disappears. Therefore, the peeling of the brown ring can be suppressed, and the yield of the silicon single crystal can be improved.

In the present invention, the maximum value of the total concentration of Na, K, and Ca in the second surface layer portion is preferably 2 times or more and 19 times the maximum value of the total concentration of Na, K, and Ca in the first surface layer portion. the following. Thereby, the generation and growth of the brown ring nucleus can be suppressed.

The maximum value of the total concentration of Na, K, and Ca in the third surface layer portion is preferably 0.6 to 1 times the maximum value of the total concentration of Na, K, and Ca in the first surface layer portion. In this case, the total concentration gradient of Na, K, and Ca in the third surface layer portion is preferably a negative gradient when the depth direction is positive, and more preferably -8.2×10 ¹⁰ atoms/cc/μm or less. gradient. Thereby, melting of the inner surface of the crucible can be suppressed, brown rings can be stably grown, and peeling from the inner surface can be suppressed.

In the present invention, the average value of the total concentration of Li, Al, Na, K, and Ca within a depth range of 0 μm or more and 8 μm or less from the inner surface is preferably 3.6×10 ¹⁶ atoms/cc or more and 5.5×10 ¹⁷ . Atom/cc or less. Since Li, Al, Na, K, and Ca have the effect of promoting the formation of brown ring nuclei, when there is a lot of Li, Al, Na, K, and Ca near the inner surface of the crucible that is initially in contact with the silicon melt, It is easy to generate brown ring nuclei on the inner surface of the crucible, resulting in poor yield of silicon single crystal. However, when the total concentration of Li, Al, Na, K, and Ca in the depth range from 0 μm to 8 μm from the inner surface of the crucible is suppressed to 5.5×10 ¹⁷ atoms/cc or less, the brown ring can be suppressed. The generation of nuclei can improve the yield of silicon single crystal.

The quartz glass crucible of the present invention preferably includes: a transparent layer comprising silica glass containing no bubbles and constituting the above-mentioned inner surface; and a bubble layer comprising silica glass containing a large number of bubbles and disposed on the transparent layer The outer side; and the thickness of the above-mentioned transparent layer is 1 mm or more. Thereby, it can prevent the brown ring peeling due to the expansion and rupture of the bubbles in the silica glass under the high temperature in the silicon single crystal pulling process.

Furthermore, the method for producing a quartz glass crucible of the present invention is characterized by comprising: a process for producing a quartz glass crucible by arc-melting raw quartz powder deposited on the inner surface of a rotary mold; and cleaning the inside of the quartz glass crucible with pure water. On the surface, the process of reducing the total concentration of Na, K, and Ca contained in the silica glass near the inner surface than before cleaning; and the process of etching the inner surface using a cleaning solution containing hydrofluoric acid.

According to the present invention, it is possible to manufacture a silica glass crucible for pulling a silicon single crystal having a peak of the total concentration of Na, K, and Ca within a depth range of 16 μm or more and 32 μm or less from the inner surface.

In the present invention, the specific resistance of pure water used in the process of washing the inner surface of the quartz glass crucible with pure water is preferably 17 MΩcm or more, the amount of water used is 125 liters/piece or more, and the water temperature is 45 ~99°C. As a result, the total concentration of Na, K, and Ca in the depth range from 0 μm to 8 μm from the inner surface can be reduced, and in particular, the total concentration of Li, Al, Na, K, and Ca can be produced to be 3.6×10 ¹⁶ Quartz glass crucible with atom/cc or more and 5.5×10 ¹⁷ atom/cc or less.

In the present invention, the etching amount of the inner surface is preferably 5 μm or more and 10 μm or less, whereby the peak of the total concentration of Na, K, and Ca is arranged in a depth range of 16 μm or more and 32 μm or less from the inner surface. Inside. By setting the peak of the total concentration of Na, K, and Ca within a depth range of 16 μm to 32 μm from the inner surface, it is possible to suppress the occurrence of brown ring nuclei on the inner surface of the crucible in the first half of the raw material melting process. produce. In addition, in the second half of the raw material melting process, the melting speed of the inner surface of the crucible is faster than the growth speed of the brown ring nucleus, so that the brown ring nucleus disappears.

The quartz glass crucible of the present invention has the effect of suppressing the occurrence of brown rings on the inner surface of the crucible, which are the cause of dislocation of the single crystal. The brown ring is caused by the long-term contact between the inner surface of the crucible and the high-temperature silicon melt. Therefore, it is preferable that the inner surface of the quartz crucible in contact with the high-temperature silicon melt has the impurity characteristics of the present invention, and it is particularly preferable that the bottom and/or corners of the crucible that is in contact with the high-temperature silicon melt have the impurity of the present invention characteristic. [Effect of invention]

According to the present invention, there can be provided a quartz glass crucible capable of suppressing the peeling of the brown ring and improving the yield of a silicon single crystal and a method for producing the same.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic side sectional view showing the configuration of a quartz glass crucible according to an embodiment of the present invention.

As shown in FIG. 1, a silica glass crucible 1 is a silica glass container for supporting a silicon melt, and has a cylindrical side wall portion 10a, a bottom portion 10b, and a space between the side wall portion 10a and the bottom portion 10b. Corner 10c. The bottom 10b is preferably a so-called round bottom that is gently curved, and can also be a so-called flat bottom. The corner portion 10c is located between the side wall portion 10a and the bottom portion 10b, and has a larger curvature than the bottom portion 10b. The boundary position between the side wall portion 10a and the corner portion 10c is the position where the side wall portion 10a begins to bend, and the boundary position between the corner portion 10c and the bottom portion 10b is the position where the larger curvature of the corner portion 10c begins to become the smaller curvature of the bottom portion 10b. Location.

The diameter of the quartz glass crucible 1 varies according to the diameter of the silicon single crystal ingot to be pulled, and is preferably 22 inches (about 560 mm) or more, more preferably 32 inches (about 800 mm) or more. The reason is that such a large-diameter crucible is preferably used for pulling large-scale silicon single crystal ingots with a diameter of more than 300 mm, and it is required that the quality of the single crystal will not be affected even if it is used for a long time. The wall thickness of the quartz glass crucible 1 is slightly different depending on its position. The wall thickness of the side wall portion 10a of a crucible of 22 inches or more is preferably 7 mm or more, and the wall thickness of the side wall portion 10a of a large crucible of 32 inches or more is preferably 7 mm or more. 10 mm or more. Thereby, a large amount of silicon melt can be stably maintained at high temperature.

The quartz glass crucible 1 has a two-layer structure and is provided with: a transparent layer 11, which contains silica glass without bubbles; outside of layer 11 .

The transparent layer 11 constitutes a layer on the inner surface 10i of the crucible in contact with the silicon melt, and is arranged so that the yield of the single crystal will not be reduced by the bubbles in the silica glass. The thickness of the transparent layer 11 is preferably 1-12 mm. In such a way that the transparent layer 11 will not completely disappear due to the melting loss in the pulling process of the single crystal and cause the bubble layer 12 to be exposed, each part of the crucible is set as appropriate thickness. The transparent layer 11 is preferably provided on the entire crucible from the side wall portion 10a to the bottom portion 10b of the crucible similarly to the bubble layer 12, but may be omitted from the upper end portion (edge portion) of the crucible that is not in contact with the silicon melt. Transparent layer 11 .

The transparent layer 11 is a portion inside the crucible where the bubble content is 0.1 vol% or less. The term that the transparent layer 11 "does not contain bubbles" means that it has a bubble content rate and a bubble size to such an extent that the single crystal yield is not reduced due to the bubbles. When the bubbles exist near the inner surface of the crucible, the bubbles near the inner surface of the crucible cannot be enclosed in the silica glass by the melting loss of the inner surface of the crucible. The bubbles in the silica glass are broken due to thermal expansion, causing the possibility of peeling off the crucible fragments (quartz pieces). When the crucible fragments released into the silicon melt are convectively transported by the melt to the growth interface of the single crystal and integrated into the single crystal, it becomes the cause of the dislocation of the single crystal. In addition, when the bubbles released into the molten liquid due to the melting loss of the inner surface of the crucible float up to the solid-liquid interface and are incorporated into the single crystal, it becomes a cause of pinholes. The average diameter of the bubbles in the transparent layer 11 is preferably 100 μm or less.

The bubble layer 12 is a layer that constitutes the outer surface 10o of the crucible, and its purpose is to improve the heat preservation of the silicon melt in the crucible, and to disperse the radiant heat from the heater to heat the silicon melt in the crucible as uniformly as possible. The above heater is installed in the single crystal pulling device so as to surround the crucible. Therefore, the bubble layer 12 is provided on the entire crucible from the side wall portion 10a to the bottom portion 10b of the crucible. The thickness of the bubble layer 12 is a value obtained by subtracting the thickness of the transparent layer 11 from the wall thickness of the crucible, and varies depending on the position of the crucible.

The air bubble content of the air bubble layer 12 is higher than that of the transparent layer 11, preferably more than 0.1 vol% and 5 vol% or less, and more preferably 1 vol% or more and 4 vol% or less. The reason for this is that if the air bubble content of the air bubble layer 12 is 0.1 vol% or less, the heat preservation function required by the air bubble layer 12 cannot be exhibited. In addition, when the bubble content rate of the bubble layer 12 exceeds 5 vol%, the crucible may be deformed by the expansion of the bubbles, resulting in a decrease in the yield of single crystals, and further, insufficient heat transfer properties. In particular, when the air cell content of the air cell layer 12 is 1 to 4%, the balance between heat retention and heat transfer performance is good, which is preferable. The bubble content rate of the bubble layer 12 can be calculated|required by measuring the specific gravity of the opaque silica glass piece cut out from a crucible, for example.

In order to prevent contamination of the silicon melt, it is desirable that the silica glass constituting the transparent layer 11 has a high purity. Therefore, the quartz glass crucible 1 of this embodiment preferably includes a synthetic quartz glass layer formed of synthetic quartz powder and a natural quartz glass layer formed of natural quartz powder. Synthetic quartz powder can be produced by vapor-phase oxidation of silicon tetrachloride (SiCl ₄ ) (dry synthesis method) or hydrolysis of silane oxides (sol-gel method). In addition, the natural quartz powder is a quartz powder produced by pulverizing a natural mineral mainly composed of α-quartz to make it into a granular form.

As described in detail below, a two-layer structure of a synthetic quartz glass layer and a natural quartz glass layer can be produced by depositing natural quartz powder along the inner surface of a crucible manufacturing mold and depositing synthetic quartz powder thereon. , the quartz powder is melted by Joule heat of arc discharge. In the initial stage of the arc melting process, the transparent layer 11 is formed by removing air bubbles by strongly vacuuming from the outside of the deposited layer of quartz powder. Thereafter, the bubble layer 12 is formed on the outer side of the transparent layer 11 by stopping or weakening the evacuation. Therefore, the boundary surface between the synthetic silica glass layer and the natural silica glass layer is not necessarily the same as the boundary surface between the transparent layer 11 and the bubble layer 12 , but the synthetic silica glass layer preferably has the same process as the transparent layer 11 that will not be pulled due to crystallization. The thickness of the inner surface of the crucible to the extent that the melting loss completely disappears.

2 is a graph showing the change in the depth direction of the total concentration of Na, K, and Ca contained in the silica glass of the surface layer portion X on the inner surface 10i side of the silica glass crucible 1 of FIG. 1, and the horizontal axis shows The position in the depth direction from the inner surface 10i of the crucible, and the vertical axis represents the total concentration of Na, K, and Ca.

As shown in FIG. 2, the quartz glass crucible 1 of the present embodiment is characterized in that the impurity concentration of the _first surface layer portion Z1 at a depth of 0 to 16 μm from the inner surface 10i of the crucible is relatively low, The impurity concentration of the second surface layer portion Z ₂ having a depth of 16 to 32 μm from the inner surface 10i is relatively high, and the impurity concentration of the third surface layer portion Z ₃ of the depth of 32 to 1000 μm from the inner surface 10i is relatively low. The total concentration of Na, K, and Ca contained in the silica glass constituting the crucible does not have a peak concentration at the position of the inner surface 10i of the crucible in the depth direction, but is 10i 32 μm or less from the inner surface, More preferably, it has a peak within a depth range of 16 to 32 μm from the inner surface 10i. The peak value of the total concentration of Na, K, and Ca within the depth range of 10i 16 to 32 μm from the inner surface is 2 of the average value of the total concentration of Na, K, and Ca within the depth range of 10i 0 to 8 μm from the inner surface ~19 times.

The first surface layer portion Z1 with _a depth of 0 to 16 μm from the inner surface 10i of the crucible is the layer initially in contact with the silicon melt, and the first half of the raw material melting process in which the _first surface layer portion Z1 is in contact with the silicon melt In (I), the nuclei of cristobalite are mostly generated on the inner surface 10i of the crucible. Metal impurities such as Li, Al, Na, K, and Ca existing near the inner surface of the crucible help to generate brown ring nuclei and become an important factor for generating more brown rings. Therefore, the average value of the total concentration of Li, Al, Na, K, and Ca within a depth range of 10i 0 to 8 μm from the inner surface of the crucible is preferably 3.6×10 ¹⁶ atoms/cc or more and 5.5×10 ¹⁷ atoms/cc the following. Thereby, the generation number of the brown ring nucleus can be reduced.

The inner surface 10i needs to be particularly provided on the bottom 10b or the corner 10c of the quartz glass crucible 1 when the concentration of impurities such as Na is reduced. The reason is that the time for the bottom 10b or the corners 10c of the quartz glass crucible 1 to be in contact with the silicon melt is longer than the time for the side wall 10a to be in contact with the silicon melt, which is a part where brown rings are likely to occur. In the side wall portion 10a, the inner surface 10i in which the impurity concentration such as Na is reduced may be provided, or the inner surface 10i in which the impurity concentration such as Na is reduced may not be provided.

It is desirable that the inner surface 10i of the crucible be as smooth as possible, especially the arithmetic mean roughness Ra of the inner surface 10i of the bottom 10b of the crucible is preferably 0.02-0.3 μm. Thereby, the number of generation of brown ring nuclei occurring in the first half (I) of the raw material melting process can be reduced.

The number of brown ring nuclei reached a peak in a certain period and then decreased sharply, and then transferred to the growth stage of brown ring nuclei. Therefore, even if the total concentration of Na, K, and Ca is slightly higher after that, the number of generated brown ring nuclei will not be greatly increased. In the second half (II) of the raw material melting process, the nucleus grows little by little to generate a brown ring. However, when the peak value of the total concentration of Na, K, and Ca in the depth range of 16 to 32 μm from the inner surface 10i is set as the concentration of Na, K, and Ca in the depth range of 0 to 8 μm from the inner surface 10i When the average concentration of the total concentration (reference concentration) is 2 to 19 times, the melting rate of the inner surface 10i of the crucible can be faster than the growth rate of the brown ring nucleus, so that the brown ring nucleus disappears.

It is known that Na, K and Ca in silica glass have the effect of promoting the melting of silica glass. In this embodiment, the total concentration of Na, K, and Ca within the depth range of 16 to 32 μm from the inner surface 10i is relatively high, so that the melting rate of the inner surface 10i of the crucible can be made faster than the growth rate of the brown ring. Fast, it can disappear before the brown ring nucleus grows up, so that the brown ring nucleus can be eliminated.

As described above, by making the total concentration of Na, K, and Ca in the _first surface layer part Z1 relatively low and by making the total concentration of Na, K, and Ca in the _second surface layer part Z2 relatively high, a certain To some extent reduce the number of brown rings. However, it is not easy to completely disappear the brown ring, and some brown rings may be formed on the inner surface 10i of the crucible. In the pulling process (III) of the silicon single crystal, the brown ring grows, so the risk of brown ring peeling becomes high. In this embodiment, since the depth from the inner surface 10i exceeds 32 μm, the average value of the total concentration of Na, K, and Ca in the deeper range (in the range of 32 to 1000 μm) is 0.6 to 1 of the reference concentration. Therefore, the melting of the inner surface 10i of the crucible in the single crystal pulling process can be suppressed. In addition, the total concentration of Na, K, and Ca in the depth range of 32 to 1000 μm from the inner surface of the crucible has a negative concentration gradient of 8.2×10 ¹⁰ atoms/cc/μm or less when the depth direction is the positive direction. Therefore, the rapid change of the total concentration of Na, K, and Ca can be suppressed, and the brown ring can be stably grown, thereby suppressing the peeling of the brown ring.

FIG. 3 is a flow chart showing a method of manufacturing the quartz glass crucible 1 . FIG. 4 is a schematic view for explaining a method of manufacturing the quartz glass crucible 1 by the rotary mold method. 5(a) to (c) are diagrams for explaining the method of manufacturing the quartz glass crucible 1, and are graphs showing the impurity concentration distribution in the depth direction from the crucible inner surface 10i.

As shown in FIGS. 3 and 4 , in the production of the quartz glass crucible 1 , first, the quartz glass crucible 1 is produced by the rotary mold method (step S11 ). In the rotating mold method, a mold 14 having a mold cavity conforming to the outer shape of the crucible is prepared, and along the inner surface 14i of the rotating mold 14, natural quartz powder 16B and synthetic quartz powder 16A are sequentially deposited to form a deposition layer of raw quartz powder. 16. It is also possible to use only natural quartz powder 16B as the raw material of the crucible. These raw quartz powders remain in a fixed position in a state of being adhered to the inner surface 14i of the mold 14 due to centrifugal force, and maintain the shape of a crucible. The wall thickness of each part of the crucible can be adjusted by changing the thickness of the deposited layer 16 of the raw quartz powder.

Next, an arc electrode 15 is installed in the mold 14, and the deposition layer 16 of the raw quartz powder is arc-melted from the inner surface 14i side of the mold 14. Specific conditions such as heating time and heating temperature need to be appropriately determined in consideration of conditions such as the raw material and size of the crucible. At this time, the deposition layer 16 of raw quartz powder is sucked from the plurality of vent holes 14a provided on the inner surface 14i of the mold 14, thereby controlling the amount of air bubbles in the molten glass. Specifically, when the arc melting is started, the suction force from the plurality of vent holes 14a provided on the inner surface 14i of the mold 14 is enhanced to form the transparent layer 11, and after the transparent layer 11 is formed, the suction force is weakened to form the bubble layer 12 .

The arc heat is gradually transferred from the inside to the outside of the deposition layer 16 of the raw quartz powder to melt the raw quartz powder. Therefore, the transparent layer 11 and the bubble layer 12 can be formed respectively by changing the decompression conditions when the raw quartz powder begins to melt. If the reduced pressure melting is carried out at the point of melting the quartz powder, the arc atmosphere gas will not be enclosed in the glass, and it will be a silica glass without bubbles. In addition, if normal melting (atmospheric pressure melting) with reduced pressure reduction is performed at the time of melting the raw quartz powder, the arc atmosphere gas will be enclosed in the glass, resulting in silica glass containing many bubbles. During reduced-pressure melting or normal melting, the thickness of each portion of the transparent layer 11 or the bubble layer 12 can be adjusted by partially changing the melting amount by, for example, changing the arrangement of the arc electrode 15 or the current.

After that, the arc heating was terminated, and the crucible was cooled. Through the above operations, the quartz glass crucible 1 in which the transparent layer 11 and the bubble layer 12 are sequentially arranged from the inner side to the outer side of the crucible wall is completed. The impurity concentration distribution in the depth direction from the inner surface 10i of the quartz glass crucible 1 thus produced after arc melting (before cleaning) is shown in FIG. At this time, the atomic radius of Li is smaller than that of other impurity elements, and it is easy to move in the glass, so it swims to the inner surface 10i side of the crucible on the arc electrode side, and the concentration is high and concentrated in a wide area in the depth direction. In addition, the Al oxide (Al ₂ O ₃ ) has a higher boiling point than the oxides of other impurity elements, so it is easy to remain on the inner surface 10i of the crucible after the quartz is sublimated, and the concentration is high like Li and concentrated in the depth direction. wider area.

Next, the inner surface 10i of the quartz glass crucible 1 is washed with pure water (step S12). Preferably, the specific resistance of the pure water used at this time is 17 MΩcm or more, the flow rate is 50 to 60 liters/min, the amount of water used in each quartz glass crucible is 125 liters or more (125 liters/piece), and the water temperature is 45～99℃. As a result, Li, Na, K, and Ca, which are easily dissolved in pure water, are eluted from the vicinity of the inner surface 10i of the crucible, and the impurity concentration in the silica glass is reduced compared with that before cleaning. As a result, the impurity concentration distribution in the depth direction from the inner surface 10i of the quartz glass crucible 1 is shown in FIG. The concentration of Al did not change significantly, and maintained a substantially constant concentration in the depth direction. The range near the inner surface 10i where the concentration of impurities such as Li is reduced is determined according to the relationship with the etching amount of the inner surface 10i, and is not particularly limited. The wide range is preferably 10i 0 to 37 μm from the inner surface.

The water temperature of the pure water used for the pure water washing is preferably 45 to 99°C, and particularly preferably 55 to 65°C in consideration of ease of operation and safety. When the water temperature of pure water is about 25 to 35°C, the effect of reducing the total concentration of Li, Na, K, and Ca in the inner surface 10i of the crucible cannot be obtained. However, by deliberately heating pure water above 45°C, Li, Na, K, and Ca can be dissolved out from the inner surface 10i of the crucible, thereby reducing the impurity concentration in the silica glass. In this way, by using high-temperature pure water, the impurities on the inner surface of the crucible can be dissolved in the pure water for washing, and the peak of the impurity concentration can be formed in a region slightly deeper than the outermost surface.

Next, the inner surface 10i of the quartz glass crucible 1 is etched using a cleaning solution containing hydrofluoric acid, thereby removing the surface layer portion of the inner surface 10i of the crucible (step S13). At this time, the etching amount of the inner surface is preferably 5-10 μm. By this etching, the inner surface 10i of the crucible can be purified, and the impurity concentration distribution in the depth direction from the inner surface 10i of the quartz glass crucible 1 is shown in FIG. The position of the peak of the total concentration was adjusted to be within the range of 16 to 32 μm 10i from the inner surface. In hydrofluoric acid cleaning, by shortening or extending the cleaning time, the etching amount on the inner surface 10i of the crucible can be changed, and by changing the etching amount, the peak position or peak height of the impurity concentration can be adjusted.

Finally, the entire quartz glass crucible 1 is finally washed with pure water (step S14). In the final cleaning, it is necessary to perform pure water cleaning under the condition that the position of the peak of the total concentration of Na, K, and Ca does not change greatly. Therefore, it is necessary to shorten the washing time and lower the water temperature to suppress the elution of Na, K, and Ca. Through the above operations, the quartz glass crucible 1 of the present embodiment is completed.

Normally, the impurity concentration on the inner surface 10i of the quartz glass crucible 1 produced by arc melting becomes the highest due to the surface concentration effect. Therefore, due to the action of impurities, brown-ring nuclei are easily generated on the inner surface of the crucible, and further, the generated brown-ring nuclei tend to grow. However, by shifting the peak position of the total concentration of Na, K, and Ca, which contributes to the production of brown ring nuclei or the melting of the crucible, to a position deeper than the inner surface of the crucible as shown in this embodiment, the number of brown ring nuclei can be reduced. The number of generated, and, to eliminate the generated brown ring nucleus. Therefore, the probability of brown ring peeling in the pulling process of the silicon single crystal can be reduced, thereby improving the yield of the single crystal.

FIG. 6 is a flowchart showing the pulling process of the silicon single crystal by the CZ method using the quartz glass crucible 1 .

As shown in FIG. 6 , the pulling process of silicon single crystal includes: a raw material melting process S21, in which the polycrystalline silicon raw material in the quartz glass crucible 1 is melted to generate a silicon melt; a liquid contacting process S22, in which the seed crystal and the silicon melt are melted. After contact with the liquid, the state is maintained for a certain period of time to make the seed crystals have affinity with the silicon melt; in the necking process S23, the diameter of the crystals is narrowed so as to eliminate the dislocation in the seed crystals due to thermal shock, etc.; In the growth process S24, the crystal diameter is gradually increased to obtain a single crystal with a predetermined crystal diameter (for example, about 300 mm); in the straight body growth process S25, the predetermined crystal diameter is maintained; in the tail growth process S26, the crystal diameter is increased The narrowing is finer, and the single crystal is cut from the molten liquid surface to complete the pulling; and the cooling process S27 is to cool the single crystal cut from the silicon molten liquid.

In the first half of the raw material melting process S21 , brown ring nuclei are generated on the inner surface 10i of the quartz glass crucible 1 in contact with the silicon melt. However, since the total concentration of Na, K, and Ca in the quartz glass crucible ₁ of the present embodiment within a depth range of 10i 0 to 8 μm from the inner surface of the crucible (in the first surface layer portion Z1) is low, it can be reduced The number of brown ring nuclei occurring in the first half of the raw material melting process S21.

In the second half of the raw material melting process S21, the brown ring nucleus grows. However, in the quartz glass crucible 1 of the present embodiment, the total concentration of Na, K, and Ca in the depth range of 16 to 32 μm from the inner surface of the crucible 10i (in the second surface layer portion Z ₂ ) is high, and the second surface layer portion has a high total concentration of Na, K, and Ca. The peak value of the total concentration of Na, K, and Ca in Z2 is ₂ to 19 times the average value of the total concentration of Na, K, and Ca in the _first surface layer part Z1, so that the melting of the inner surface 10i of the crucible can be accelerated. , the melting speed of the inner surface 10i of the crucible is faster than the growth speed of the brown ring. Therefore, the brown ring nuclei generated in the first half of the raw material melting process can be eliminated and the number of brown rings generated can be reduced.

In the growth process of the silicon single crystal from the necking process S23 to the tail growth process S26, not only the brown ring grows, but also a part of the brown ring may peel off, and a part of the brown ring peeled off from the inner surface 10i is melted When the liquid is convectively transported to the solid-liquid interface, there is a risk of dislocation of the silicon single crystal. However, the total concentration of Na, K, and Ca in the depth range of 32 to 1000 μm from the inner surface of the crucible (in the third surface layer portion Z ₃ ) is low, and the Na, K, and Ca in the third surface layer portion Z ₃ are low. The average value of the total concentration is 0.6 times or more and not more than 1 time the average value of the total concentration of Na, K, and Ca in the _first surface layer portion Z1, so that excessive melting of the inner surface 10i of the crucible can be suppressed. In addition, since the rate of change of the total concentration of Na, K, and Ca in the _third surface layer portion Z3 is small, in particular, the total concentration gradient of Na, K, and Ca is -8.2×10 ¹⁰ atoms/cc/μm or more and does not 0 atoms/cc/μm, so the peeling of the brown ring caused by the sudden change of the state of the inner surface 10i of the crucible can be suppressed.

The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention, which are of course also included in the scope of the present invention. . [Example]

Prepare samples A1-A8 of 32-inch quartz glass crucibles. After the quartz glass crucible was manufactured by the rotary mold method as described above, pure water washing, hydrofluoric acid washing, and final washing were performed in this order. As described above, in the pure water washing, the specific resistance of the pure water used is set to 17 MΩcm or more, the flow rate is set to 50 to 60 liters/min, and the amount of water used per quartz glass crucible is set to 150 liters , and set the water temperature to 55 to 65°C. In addition, in the hydrofluoric acid cleaning, the etching amount of the inner surface was set to about 8 μm. The distribution in the depth direction of the total concentration of Na, K, and Ca near the inner surface of the crucible (peak position and concentration ratio of the total concentration) can be adjusted by changing the hydrofluoric acid cleaning time (etching amount).

Next, the arithmetic mean roughness Ra (μm) of the inner surfaces of the samples A1 to A8 of the quartz glass crucible was measured. In addition, in order to evaluate the impurity concentration of the extreme surface layer portion of the inner surface of the quartz glass crucible, a sample of the silica glass sheet of the extreme surface layer portion was collected by the SAICAS (Surface And Interfacial Cutting Analysis System) method.

FIG. 7 is a schematic diagram showing the principle of the SICAS method.

As shown in FIG. 7 , in the SAICAS method, an oblique cutting device 20 is used to move the cutting blade 21 in the horizontal direction D _X and the vertical direction D _Y , and the polar surface layer portion on the inner surface 10i side of the quartz glass crucible 1 is cut. By slicing it obliquely, a silicon dioxide glass sheet can be used, so the detection area of the impurity concentration using D-SIMS can be increased, and the detection sensitivity can be obtained. Therefore, the impurity concentration distribution of the polar surface layer portion of the quartz glass crucible 1 can be analyzed with high sensitivity.

Figures 8(a) and (b) are images of the silica glass sheet taken by the SAICAS method, Figure 8(a) shows a part of the inner surface of the crucible after cutting the silica glass sheet, Figure 8( b) represents the silica glass piece cut from the inner surface of the crucible. A sample of the silica glass sheet has a width of about 50 μm, a length of about 500 μm, and a cut-in depth of about 50 μm. As such, the samples are very elongated relatively thin sheets of silica glass.

Next, the total concentration of Na, K, and Ca contained in the silica glass sheets of the samples A1 to A8 of the quartz glass crucible was measured by D-SIMS (Dynamic-Secondary Ion Mass Spectrometry: dynamic secondary ion mass spectrometry). The samples shown in Fig. 8(b) were used for the measurement of the impurity concentration, and the depths from the inner surface of the crucible were 0-8 μm (a part of the range of the first surface layer part Z ₁ ) and 16-32 μm (the first surface layer part Z 1 ). 2 surface layer part Z ₂ ), 32-500 mm (3rd surface layer part Z ₃ ) position. Then, the total concentration ratio of Na, K, and Ca ([II/I]), the total concentration ratio of Na, K, and Ca ([III/I]), and the Na in the _third surface layer portion Z3 were obtained by calculation. , K, Ca total concentration gradient. Furthermore, the ratio of the total concentration of Na, K, and Ca ([II/I]) is the peak value (II) of the total concentration of Na, K, and Ca in the Z2 region of the _second surface layer relative to the peak value (II) of the total concentration of Na, K, and Ca from the inner surface of the crucible. The ratio of the average value (I) of the total concentration of Na, K, and Ca in the depth range of 0 to 8 μm. In addition, the ratio of the total concentration of Na, K, and Ca ([III/I]) is the average value (III) of the total concentration of Na, K, and Ca in the region Z3 of the _third surface layer relative to the average value (III) of the total concentration of Na, K, and Ca from the inner surface of the crucible. The ratio of the average value (I) of the total concentration of Na, K, and Ca in the depth range of 0 to 8 μm.

Next, samples of other quartz glass crucibles produced under the same conditions as the quartz glass crucible samples A1 to A8 were prepared, and the silicon single crystal was actually pulled. After the pulling process was completed, the number density (pieces/cm ² ) of brown rings produced on the inner surface of the quartz glass crucible was evaluated. In addition, the delay time (hr) and the single crystal yield (%) of the silicon single crystal were evaluated. Furthermore, the delay time (hr) refers to the time difference from the start of the initial neck process to the start of the final neck process when one silicon single crystal is manufactured. When the single crystal is normally produced without re-pulling the single crystal, the delay time is 0 hr. In addition, the single crystal yield is a value calculated by (single crystal weight after cylindrical grinding)÷(silicon raw material weight)×100%.

FIG. 9 is a table summarizing the evaluation conditions and results of the samples A1 to A8 with the quartz glass crucibles.

As shown in FIG. 9 , in Examples 1 to 4 (samples A1 to A4), the concentration ratio ([II/I]) of the second surface layer portion Z ₂ was 2 to 19, and the concentration ratio of the third surface layer portion Z ₃ was 2 to 19. ([III/I]) is 0.6 to 1.0, and the concentration gradient of the third surface layer portion Z ₃ is -8.5×10 ¹⁰ to -8.6×10 ¹¹ atoms/cc/μm. In addition, the arithmetic mean roughness of the inner surface of the bottom of the crucible is 0.02 to 0.03 μm. In addition, the number density of brown rings on the inner surface of the used crucible after pulling the silicon single crystal was 2 pieces/cm ² or less, and the peeled area ratio was 8% or less, which were generally good results. Furthermore, the pulling result of the silicon single crystal is not delayed, and the single crystal yield rate is over 80%.

In Comparative Example 1 (Sample A5), the concentration ratio ([II/I]) of the second surface layer part Z ₂ was 1, the concentration ratio ([III/I]) of the third surface layer part Z 3 was 0.1, and the third surface layer part Z ₃ had a concentration ratio ([III/I]) of 0.1. The concentration gradient of the surface layer portion Z ₃ was -2.9×10 ¹⁰ atoms/cc/μm. In addition, the arithmetic mean roughness of the outermost surface was 0.03 μm. In addition, the number density of brown rings on the inner surface of the used crucible after pulling the silicon single crystal was 5 pieces/cm ² , and the peeling area ratio was 26%. Furthermore, regarding the pulling result of the silicon single crystal, the delay time was 15.3 hr, and the single crystal yield was 35.1%. In sample A5, since the total concentration of Na, K, and Ca in the second surface layer portion Z ₂ is relatively low, and the total concentration of Na, K, and Ca in the second surface layer portion Z ₂ is very low, it is considered to be the brown ring. The number of occurrences and the peeling area ratio increase, resulting in the occurrence of dislocation of the single crystal.

In Comparative Example 2 (Sample A6), the concentration ratio ([II/I]) of the second surface layer portion Z ₂ was 1, the concentration ratio ([III/I]) of the third surface layer portion Z 3 was 0.1, and the third surface layer portion Z ₃ had a concentration ratio ([III/I]) of 0.1. The concentration gradient of the surface layer portion Z ₃ was -8.6×10 ¹¹ atoms/cc/μm. In addition, the arithmetic mean roughness of the outermost surface was 0.02 μm. In addition, the number density of brown rings on the inner surface of the used crucible was 6 pieces/cm ² , and the peeling area ratio was 31% or less. Furthermore, regarding the pulling result of the silicon single crystal, the delay time was 5.3 hr, and the single crystal yield was 51.5%. Also in sample A6, since the total concentration of Na, K, and Ca in the second surface layer portion Z ₂ is relatively low, and further the total concentration of Na, K, and Ca in the second surface layer portion Z ₂ is very low, it is considered to be a brown ring. The number of occurrences and the peeling area ratio increase, resulting in dislocation of the single crystal.

In Comparative Example 3 (Sample A7), the concentration ratio ([II/I]) of the second surface layer portion Z ₂ was 2, the concentration ratio ([III/I]) of the third surface layer portion Z 3 was 0.1, and the third surface layer portion Z ₃ had a concentration ratio ([III/I]) of 0.1. The concentration gradient of the surface layer portion Z ₃ was -5.9×10 ¹⁰ atoms/cc/μm. In addition, the arithmetic mean roughness of the outermost surface was 0.04 μm. In addition, the number density of brown rings on the inner surface of the used crucible was 2 pieces/cm ² , and the peeling area ratio was 42%. Furthermore, with regard to the pulling result of the silicon single crystal, there was no delay, but the single crystal yield was 60.5%. In sample A7, since the total concentration of Na, K, and Ca in the second surface layer portion Z ₂ is very low, it is considered that the dislocation of the single crystal is caused by an increase in the peeled area ratio of the brown ring.

In Comparative Example 4 (Sample A8), the concentration ratio ([II/I]) of the second surface layer portion Z ₂ was 21, the concentration ratio ([III/I]) of the third surface layer portion Z 3 was 0.8, and the third surface layer portion Z ₃ had a concentration ratio ([III/I]) of 0.8. The concentration gradient of the surface layer portion Z ₃ was -4.3×10 ¹⁰ atoms/cc/μm. In addition, the arithmetic mean roughness of the outermost surface was 0.05 μm. In addition, the number density of brown rings on the inner surface of the used crucible was 1 piece/cm ² , and the peeling area ratio was 36%. Furthermore, with regard to the pulling result of the silicon single crystal, there was no delay, but the single crystal yield was 45.9%. In sample A8, since the total concentration of Na, K, and Ca in the second surface layer portion Z ₂ is relatively high, it is considered that the number of occurrences of brown rings and the peeling area ratio increase, resulting in the dislocation of the single crystal.

1: Quartz glass crucible 10a: Side wall 10b: Bottom 10c: Corner 10i: Inner surface 10o: Outer surface 11: Transparent layer 12: Bubble layer 14: Mold 14a: Ventilation hole 14i: Inner surface of mold 15: Arc electrode 16 : deposited layer 16A: synthetic quartz powder 16B: natural quartz powder 20: oblique cutting device 21: cutting blade D _X : horizontal direction D _Y : vertical direction S11: crucible manufacturing step S12: pure water washing step S13: hydrofluoric acid Cleaning (etching) step S14: Final cleaning step S21: Raw material melting process S22: Liquid contacting process S23: Necking process S24: Shoulder growth process S25: Straight body growth process S26: Tail growth process S27: Cooling process X : Surface layer part Z ₁ : First surface layer part Z ₂ : Second surface layer part Z ₃ : Third surface layer part

FIG. 1 is a schematic side sectional view showing the configuration of a quartz glass crucible according to an embodiment of the present invention. Fig. 2 is a graph showing the change in the depth direction of the total concentration of Na, K, and Ca contained in the silica glass in the surface layer portion on the inner surface side of the silica glass crucible of Fig. 1, and the horizontal axis represents the depth from the crucible. The position in the depth direction from the inner surface, and the vertical axis represents the total concentration of Na, K, and Ca. Fig. 3 is a flow chart showing a method of manufacturing a quartz glass crucible. FIG. 4 is a schematic view for explaining a method of manufacturing a quartz glass crucible by a rotary mold method. FIGS. 5( a ) to ( c ) are diagrams for explaining a method of manufacturing a quartz glass crucible, and are graphs showing the impurity concentration distribution in the depth direction from the inner surface of the crucible. FIG. 6 is a flowchart showing a pulling process of a silicon single crystal by the CZ method using a quartz glass crucible. FIG. 7 is a schematic diagram showing the principle of the SICAS method. Figures 8(a) and (b) are images of the silica glass sheet taken by the SAICAS method, Figure 8(a) shows a part of the inner surface of the crucible after cutting the silica glass sheet, Figure 8(b) ) represents a piece of silica glass cut from the inner surface of the crucible. FIG. 9 is a table summarizing the evaluation conditions and results of the samples A1 to A8 with the quartz glass crucibles.

1: Quartz glass crucible

10a: Side wall portion

10b: Bottom

10c: Corner

10i: inner surface

10o: outer surface

11: Transparent layer

12: bubble layer

X: surface layer

Claims (10)

A quartz glass crucible, characterized in that the peak of the distribution of the total concentration of Na, K, and Ca in the depth direction from the inner surface exists within a depth range of 32 μm or less from the inner surface. The quartz glass crucible according to claim 1, wherein the peak of the total concentration of Na, K, and Ca exists within a depth range of 16 μm or more and 32 μm or less from the inner surface. The quartz glass crucible of claim 2, wherein the peak of the total concentration of Na, K, and Ca within a depth range of 16 μm to 32 μm from the inner surface is the Na, K within a depth range of 0 μm to 8 μm from the inner surface. , 2 times or more and 19 times or less the average value of the total concentration of Ca. The quartz glass crucible according to claim 2 or 3, wherein the average value of the total concentration of Na, K, and Ca within a depth range of 32 μm to 1000 μm from the inner surface is 0 μm to 8 μm from the inner surface. 0.6 times or more of the average value of the total concentration of Na, K, and Ca and not more than 1 time. The quartz glass crucible according to claim 4, wherein the total concentration of Na, K, and Ca within the depth range of 32 μm to 1000 μm from the inner surface has a negative concentration gradient when the depth direction is the positive direction. The quartz glass crucible according to claim 2 or 3, wherein the average value of the total concentration of Li, Al, Na, K, and Ca within the depth range of 0 μm to 8 μm from the inner surface is 3.6×10 ¹⁶ atoms/cc or more and 5.5 ×10 ¹⁷ atoms/cc or less. The quartz glass crucible according to any one of claims 1 to 3, comprising: a transparent layer comprising silica glass containing no bubbles, constituting the above-mentioned inner surface; and a bubble layer comprising silica glass containing a large number of bubbles The glass is arranged on the outer side of the transparent layer; and the thickness of the transparent layer is 1 mm or more. A method for manufacturing a quartz glass crucible, which is characterized by comprising: a process of arc melting raw quartz powder deposited on the inner surface of a rotating mold to manufacture a quartz glass crucible; A process in which the total concentration of Na, K, and Ca contained in the silica glass near the inner surface is lower than that before cleaning; and a process in which the inner surface is etched using a cleaning solution containing hydrofluoric acid. The method for producing a quartz glass crucible according to claim 8, wherein the specific resistance of the pure water used in the process of washing the inner surface of the quartz glass crucible with pure water is 17 MΩcm or more, and the amount of water used is 125 liters or more, The water temperature is 45~99℃. The method for producing a quartz glass crucible according to claim 8 or 9, wherein the etching amount of the inner surface is 5 μm or more and 10 μm or less, whereby the peak of the total concentration of Na, K, and Ca is placed at a distance of 16 μm or more and 32 μm or less from the inner surface. within the depth range.

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